We have previously isolated and identified two gulathione conjugates of bromobenzene as trans-3-bromo-6(glutathion-S-yl)-cyclohexa-2, 4-dien-1-01 (BB-GSHA) and trans-4-bromo-6(glutathion-S-yl)-cyclohexa-2, 4-dien-1-01 (BB-GSHB). The two conjugates are formed in unequal amounts in a ratio of BB-GSHA:BB-GSHB of 1.6:1. We have therefore purified the various forms of glutathione-S-transferease enzymes from rat liver and examined their ability to catalyze the reaction of bromobenzene-3, 4-oxide with glutathione. All forms of the enzyme isolated exhibit catalytic activity towards the epoxide. However, the ratio of the two conjugates formed with the purified enzymes varies from the ratio obtained both in vivo and with rat liver microsomes and 100,000 x g supernatant. The combined conjugates are metabolized by Grama-glutamyl transpeptidase at apparently identical rates, and give rise to five products. One of the products is less water soluble than the starting substrates and might be the dehydrated, aromatized cysteinyl glycine conjugate.